It is known to use radar probes for determining the profile of the loading surface of a shaft furnace in order to better control the running of the furnace and to optimize the loading configuration. In order to be advantageous, these probes must allow a measurement which is as accurate as possible in a minimum of time.
The document EP-Al-0,291,757 describes a radar probe which is mounted at the end of an arm inserted horizontally in the furnace above the loading surface. This probe has the advantage of being able to scan in the two opposite directions and to provide, depending on the density of the measurement positions, an image which is sufficiently representative of the entire loading surface. The disadvantage of this probe is that the loading must be interrupted, not only during the period of the measurement, but also during the insertion and withdrawal of the probe arm. This arm also requires a relatively large mechanical structure. Another disadvantage of this probe is that it is relatively close to the loading surface and that the radar beams, particularly those directed towards the periphery, meet the surface at a very acute angle which makes the processing of the measurement results difficult.
Another known radar probe is that described in U.S. Pat. No. 4,332,374, the disclosure of which is incorporated herein by reference. The antenna of this radar probe is mounted in a window in the oblique wall of the furnace above the loading surface, on a support which can be moved vertically. The advantage of this probe is that it is a little more distant from the loading surface than the previous probe and that the radar beams are less oblique in comparison with the previously mentioned probe. Although the antenna can be driven in rotation about its vertical axis of suspension and can thus determine, by several successive measurements, the loading profile along a circular scanning line, it does not allow the probing of the entire loading surface. In order to be able to do this, it must be able to scan the surface in two perpendicular directions. However, the probe described in the '374 patent cannot provide a two dimensional mechanical scanning of the loading surface because this would require a large opening in the thick oblique wall of the furnace wall, associated with a window which is transparent to microwaves. In effect, such a window would reduce the mechanical strength of the wall too much and would be difficult to clean. On the other hand, the probe of the '374 patent has the advantage of requiring relatively simple mechanics.